Boom or Bust for Netflix, Amazon.com and Salesforce.com?

With these pricey stocks having more than tripled in the past five years, here's a look at long-term valuations.

Some pricey dot-com stocks have slaughtered the bears that bet against them over the past five years. Shares of Salesforce.com (ticker: CRM), whose software helps companies manage customer interactions, have tripled. Amazon.com (AMZN) stock has quadrupled. And Netflix (NFLX) has more than quintupled. The Nasdaq Composite index, for comparison, is up 43% over the past five years.

Price-to-earnings ratios make little sense for this crowd. The Standard & Poor's 500 trades at 14 times this year's earnings forecast....